SPIN-DOWN MEASUREMENT OF PSR J1852+0040 IN KESTEVEN 79: CENTRAL COMPACT OBJECTS AS ANTI-MAGNETARS

Using XMM-Newton and Chandra, we achieved phase-connected timing of the 105 ms X-ray pulsar PSR J1852+0040 that provides the first measurement of the spin-down rate of a member of the class of central compact objects (CCOs) in supernova remnants. We measure (P) over dot = (8.68 +/- 0.09) x 10(-18), and find no evidence for timing noise or variations in X-ray flux over 4.8 year. In the dipole spin-down formalism, this implies a surface magnetic field strength B-s = 3.1 x 10(10) G, the smallest ever measured for a young neutron star, and consistent with being a fossil field. In combination with upper limits on B-s from other CCO pulsars, this is strong evidence in favor of the anti-magnetar explanation for their low luminosity and lack of magnetospheric activity or synchrotron nebulae. While this dipole field is small, it can prevent accretion of sufficient fall-back material so that the observed X-ray luminosity of L-x = 5.3 x 10(33)(d/7.1 kpc)(2) erg s(-1) must instead be residual cooling. The spin-down luminosity of PSR J1852+0040, (E) over dot = 3.0 x 10(32) erg s(-1), is an order of magnitude smaller than L-x. Fitting of the X-ray spectrum to two blackbodies finds small emitting radii, R-1 = 1.9 km and R-2 = 0.45 km, for components of kT(1) = 0.30 keV and kT(2) = 0.52 keV, respectively. Such small, hot regions are ubiquitous among CCOs, and are not yet understood in the context of the anti-magnetar picture because anisotropic surface temperature is usually attributed to the effects of strong magnetic fields.